BREAKING: FDA expands COVID vaccine warning about heart side effect risk for young males

CBS News reported on Wednesday: "The Food and Drug Administration is telling Pfizer and Moderna to expand the warning labels on their COVID-19 vaccines about the risk of a possible heart injury side effect linked to the mRNA shots, primarily in teen boys and young men, citing findings from a study published last year and new agency data.

Orders to expand the warnings were posted Wednesday by the FDA, in letters dated April 17 to Pfizer and BioNTech about their Comirnaty vaccine and Moderna about its Spikevax vaccine.

Both vaccines previously carried warnings about how the risk of the heart side effects — which doctors call myocarditis (an inflammation of the heart muscle) and pericarditis (inflammation of the membrane surrounding the heart) — looked to be higher in young men, generally within the first week after vaccination. While the earlier labels specified ages 18 to 24 years old for Moderna's vaccine and 12 to 17 years old for Pfizer's, the new warning will apply to males ages 16 to 25 for both vaccines.

"Following administration of the 2023-2024 Formula of mRNA COVID-19 vaccines, the highest estimated incidence of myocarditis and/or pericarditis was in males 16 through 25 years of age," the FDA says in the new blanket warning it will require for both vaccines.

The rate of myocarditis and pericarditis was around 8 cases per million doses for children and adults under 65 years old after use of that season's vaccines, the FDA says.

The new warnings ordered by the FDA add that the "highest estimated incidence was in males 16 through 25 years of age," with a rate of 38 cases per million.

The Centers for Disease Control and Prevention has previously described rates of myocarditis and pericarditis as rare after COVID-19 vaccination. 

CDC officials told the agency's vaccine advisers last month that acute myocarditis "tends to resolve quickly" after vaccination, and no increased risk had been seen in data from recent seasons in people 12 to 39 years old.

It is unclear whether Pfizer or Moderna disputed the order. They had "within 30 calendar days of the date of this letter" to try to rebut the demand. Spokespeople for Moderna and Pfizer did not immediately respond to a request for comment."

For the full read, visit CBS News.